Field of the Invention
The present invention relates to a method for contact-connecting a semiconductor component to a metallization on a film.
With electrically conductive adhesives, electrically conductive connections can be produced even at a low processing temperature. However, for curing, many adhesives of this type actually need higher temperatures, at which the plastics material of a film is damaged or a metallization applied thereto is detached. Moreover, the electrical conductivity is insufficient for many applications, and the connection produced is sensitive to moisture. Particularly if a contact of an electronic component (e.g., an Si-IC Chip) is intended to be electrically conductively connected to a metal layer (e.g., made of copper or nickel) of a metallized plastic film, in the case of which the limit of thermal loadability is about 120xc2x0 C. and in the case of which the applied metal layer is very thin (typically about 100 nm), it is difficult, with conductive adhesive, to produce a sufficiently lasting and readily conductive connection that cannot be detached without destroying the film.
It is accordingly an object of the invention to provide a method for contact-connecting a semiconductor component to a metallized plastic film that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that can be performed at a temperature at which the film is not damaged and which yields a permanent electrically conductive connection of sufficient conductivity.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for contact-connecting a semiconductor component to a film provided with a metal layer, including the steps of disposing a solder material between a contact of the semiconductor component and the metal layer of the film, the solder material containing at least two different substances selected from a group consisting of elementary metals and semiconductor materials and having a melting point at a temperature at which the film is not damaged, and subsequently causing the solder material to melt and thereafter solidify and, thereby, produce a permanent electrically conducted connection of a material having a melting point higher than the melting point of the disposed solder material.
In accordance with another mode of the invention, a solder material, preferably, a metal, made of at least two metallic or semiconducting chemical elements is applied to a contact of the semiconducting component or to the metal layer of the film at the location provided for a contact connection. The solder material is configured such that it has a melting point that lies below a critical temperature for the resistivity of the film, and that it forms, after melting, a material that, after solidification, has a higher melting point than the original solder material. The molten solder material is, preferably, configured such that it forms an alloy or intermetallic compound or phase with the metal of the metal layer of the film or with the metal of the contact of the semiconductor component. The melting point is, preferably, so high that, in the event of an attempt to melt the solder connection, the film would inevitably be damaged or at the very least the metal layer would be detached from the film and the entire configuration would, thus, become unusable.
A solder material that is particularly suitable for such a purpose is a compositionxe2x80x94i.e., a blend of at least and, preferably, two components that form a mixture, an alloy, or a stoichiometric compoundxe2x80x94whose proportions are chosen such that the composition lies at a eutectic point or at least in the vicinity of a eutectic point. Specifically, it holds true for such a choice of the composition that the melting point of the composition increases in the event of any change in the proportions of the components. When the solder material melts, an alloy or an intermetallic compound is produced that contains a proportion of the metal of the metal layer of the film or of the contact of the semiconductor component so that the composition of the material forming the electrically conductive connection differs from the eutectic of the original composition of the solder material to such a significant extent, that the melting point is considerably higher, in particular, above the temperatures that are safe for the film. In such a case, an approximately eutectic composition shall be defined as a composition having a melting point that differs from the eutectic temperature by at most 10xc2x0 C.
In accordance with a further mode of the invention, a solder material is selected with which, in the melting and solidification step, one of an alloy and an intermetallic compound having a higher melting point is formed with a metal of the metal layer of the film.
In accordance with an added mode of the invention, the solder material, in the melting and solidification step, forms, with a metal of the metal layer of the film, one of an alloy and an intermetallic compound having a higher melting point than the melting point of the solder material.
In accordance with an additional mode of the invention, a solder material is utilized having a melting point at most 10xc2x0 C. above a temperature of a eutectic composition of the substances contained in the solder material.
A material that is appropriate as a possible solder material, preferably, in conjunction with a metal layer of the film made of copper or nickel, is primarily a material containing bismuth (chemical symbol Bi). Eutectic or approximately eutectic (difference in temperature from the eutectic at most 10xc2x0 C.) compositions that achieve what is desired are materials from the group of a composition including bismuth and indium, a composition including bismuth and tin, and a composition including indium and tin. The eutectic compositions of these materials in relative atomic masses are Bi22In78, Bi43Sn57, or In52Sn48. The material Bi22In78 forms a eutectic composition having the melting point of 72.7xc2x0 C. A solder connection can, thus, be produced at approximately 80xc2x0 C. The solder material Bi22In78 is applied, e.g., to the contact of the semiconductor component, which can be done by sputtering. The solder material, then, forms a thin layer on the contact. The layer is brought into contact with the metal layer of the film and, as required, kept under slight pressure. Through heating to a temperature above the melting point of the solder material, the solder material is melted and alloys with the metal of the metal layer of the film to form a material that forms an electrically conductive connection between the contact of the semiconductor component and the metal layer of the film that can be subjected to loading up to at least 270xc2x0 C. With the use of a film whose thermal loadability extends up to a maximum of about 120xc2x0 C., the connection can, therefore, be produced without difficulty at about 80xc2x0 C. Afterwards, the connection can no longer be melted without destroying the film.
In accordance with yet another mode of the invention, a solder material is utilized including one of an intermetallic compound of one of BiIn and BiIn2 and a phase of one of BiIn and BiIn2.
In accordance with yet a further mode of the invention, the solder material is applied in the disposing step by electron beam vaporization onto one of the contact of the semiconductor component and the metal layer of the film.
In accordance with yet an added mode of the invention, electron beam vaporization is used to apply the solder material onto one of the contact of the semiconductor component and the metal layer of the film.
In accordance with yet an additional mode of the invention, the solder material is applied in the disposing step with a layer thickness limited in comparison with a thickness of the metal layer of the film to permit at least a portion of the metal layer of the film to remain unchanged after the melting and solidification step.
In accordance with a concomitant mode of the invention, there is provided the step of insuring that at least a portion of the metal layer of the film remains unchanged after the melting and solidification step by applying the solder material with a layer thickness limited in comparison with a thickness of the metal layer of the film.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for contact-connecting a semiconductor component, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.